The continuing purpose of this project is the study of Tyzzer's disease. The topics of present interest are: (1) characterization of the causative agent, Bacillus piliformis; (2) the serological response of the host to B. piliformis infection using the complement fixation test and fluorescent antibody techniques; (3) the relationship of isolants from the rabbit and horse foal; (4) the pathogenesis of Tyzzer's disease in a variety of laboratory animals; (5) the stability of the spores of B. piliformis under a variety of conditions including temperature variation and contact with chemicals; and (6) the epidemiology of Tyzzer's disease, the goal being to identify primary sources of the infection.